Ornithologists have noted that especially during the winter, American Crows assign one or more of their flock to keep watch over the rest of the group, or “murder,” as they feed on the ground nearby. While acting as sentinels, the crows will call frequently, even when predators are not present. When they intensify their calling, the crows that are feeding often flush.
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Looking as if it were stuck to the vertical cliff wall by crazy glue, a raven’s nest is often used for several years in a row. The nestlings remain in the nest for about 5 to 7 weeks, during which time they go from being an orange/pink color, sparsely covered with gray down, to the black plumage of an adult. The pictured nestlings are approximately five weeks old, and have just started to exercise their wing muscles in preparation for their first flight. They are panting with open beaks in an attempt to dissipate the heat of an unrelenting May sun. Within a week or two they will leave the nest, but will stay nearby for a few days. I couldn’t get close enough to give this nest a smell test, but supposedly raven nests can have an unbelievably unpleasant odor (due to the remains of leftover food/ carrion and feces).
After the breeding season, American crows begin to gather in small, communal roosts. By early to mid-winter the number of crows occupying a roost reaches its maximum. In the morning, shortly before and after daybreak, crows leave their nocturnal roosts in small groups and fly in all directions leading to feeding grounds. After having spent the day feeding, roughly two to three hours before sunset, small groups of crows gather in pre-roost sites, and from these fly along regular flight lines towards their roost. They are often joined by additional crows at pre-roost sites visited along the way. The closer the crows get to their final roost, the larger the group becomes. The same roosting sites may be used for many years and the number of birds in them varies from a few hundred to many thousands.